Biomechanical Evaluation of Safe Incisions to Mitigate Failure in Tendon Repair

Abstract Background: Rupture at tendon repair sites in animal models impedes the study of healing. To address this, we investigated “safe incisions” – strategic partial transections to prevent rupture under excessive force. We hypothesized these would act as mechanical “fuses,” reducing repair site tension. Objectives: This in vitro biomechanical study optimized safe incision spacing to enhance tendon construct strength and minimize gap formation in a turkey flexor tendon model. Materials and Methods: Forty turkey flexor tendons were divided into five groups ( n = 8): Repaired without incisions, intact with 5 mm incisions, repaired with 5 mm incisions, intact with 10 mm incisions, and repaired with 10 mm incisions. Repairs used a modified Pennington suture. Safe incisions (opposing hemi-transections) with 5 mm or 10 mm longitudinal spacing were created proximally. Tendons were tested to failure at 1 mm/s, recording force-elongation, failure mode, gap formation (>2 mm at 10% strain), stiffness, and repair site elongation. Results: Repaired tendons without incisions (Group 1) showed 100% repair site failure (46.5 ± 10.96 N). With 5 mm safe incisions (Group 3), no repair site failures occurred (incision failure at 18.11 ± 10.96 N). 10 mm incisions (Group 5) offered partial protection (25% repair failure at 37.48 ± 11.35 N). Group 1 had higher gap formation (75% vs. 0% in Group 3, P < 0.01), stiffness, and repair site elongation than Groups 3 and 5. Gap formation force was similar for Group 1 (25.76 ± 9.18 N) and Group 5 (25.04 ± 12.21 N). Conclusions: In this in vitro model, 5 mm spaced safe incisions effectively shifted failure away from the repair and limited gap formation by reducing stiffness. 10 mm incisions provided partial protection. Strategically placed safe incisions show potential to protect tendon repairs from immediate rupture by enabling controlled lengthening at a weaker site. However, tendinopathy risk and clinical relevance require in vivo studies.